The present invention relates to a method of forming a lithographic printing plate from a silver halide photographic material, and more particularly to a lithographic printing plate in which a silver halide photographic image is made oleophilic and receptive to inks, and a method of forming the same.
A lithographic printing plate comprises an oleophilic image portion which is receptive to oily inks and an oil-repellent non-image portion which is not receptive to the inks. In general said non-image portion is receptive to water, i.e., hydrophilic.
A usual lithographic printing plate can be thus provided thereon with both water and ink. That is, an image portion is receptive to a coloring ink and a non-image portion receptive to water. Printing is effected by transferring the ink on the image portion onto a base such as paper. In order to make a good printing a great difference between the hydrophilicity of a non-image portion and the oleophilicity of an image portion is required, that is, when an ink is applied it is required that the image portion receives a sufficient amount of the ink and the non-image portion does not completely receive the ink. Various materials for such lithographic printing and methods of forming such printing plates are already known.
There are some requirements to small flexible printing plates for "small offset" printing used in offices. The production of these printing plates with ease, certainty and rapidity, preferably in an automatic manner is required. Prior printing plates consisting essentially of a sensitive aqueous colloid of a bichromate and a sensitive organic diazo colloid do not satisfy all of these requirements. Furthermore, they lack sensitivity in forming images by a direct optical projection.
Printing plates prepared by an electrophotographic process satisfy more of the requirements above but do not always have good reproduction of images and run strength.
A photographic material comprising a silver halide emulsion which is highly sensitive and spectrum-sensitizable is suitable for the automatic production of printing plates, and it has been used in some forms.
Typical known methods for forming lithographic printing plates by using a photographic gelatin-silver halide emulsion are as follows:
(1) a method in which a hydrophilic gelatin-silver halide emulsion is subjected to the tanning development and the developed portion of gelatin is cured to be oleophilic and receptive to inks (cf. U.S. Pat. No. 3,146,104),
(2) a method utilizing the silver complex diffusion transferring in which the formed superficial pattern of metallic silver or silver complex image is converted to be oleophilic and receptive to inks (cf. U.S. Pat. Nos. 3,721,559, 3,490,905, 3,063,837, and 3,728,114, DAS No. 1,116,536 and Journal of Photographic Science 8, 26-32, 1960, A. Rott & L. DeHaes),
(3) a method in which developed silver images or silver images formed by the transferring development are treated with a bleaching solution using etching bleach and simultaneously gelatin at the silver pattern is destroyed to expose an oleophilic surface (cf. U.S. Pat. No. 3,385,701, U.S. Pat. No. 3,814,603 and Japanese Patent Publication No. 27242/69), and
(4) a method in which an undeveloped silver halide portion in a hydrophilic gelatin-silver halide emulsion layer developed is selectively converted to be oleophilic and receptive to inks (cf. U.S. Pat. Nos. 3,454,398, 3,764,323 and 3,099,209).
However, these roughly classified methods have problems in constructions of materials or treatment originating from their principles and mechanism. For example, the printing plate shown in (1) which utilizes curing phenomenon must be treated with a developing solution containing no or a little amount of sulfite to cause the problem of reduction in image quality due to diffusion of oxides of the tanning developing agent. In the case of the method (2) which utilizes silver complex diffusion transfer process, generally the developing treatment of a high alkalinity is required, fluctuations in characteristics such as sensitivity often occur when a great number of printing is carried out and moreover there are technical limitations when automatic plate making is carried out by contact transfer method (light sensitive material and printing material are separate materials). According to the method (3) which utilizes etching bleach, a large amount of sludges occur during the treatment to make it difficult to obtain stable characteristics and moreover there has been a problem in the preservation of treating machines.
The lithographic printing plate of the present invention belongs to the field of the method (4). That is, in the case of printing plate where undeveloped silver halide image portion is made ink receptive, the so-called ordinary developing treatment can be applied, the characteristics obtained by the treatment are stable and moreover since light sensitive material and printing plate are the same it becomes easy to carry out automatic treatment.
In a method of forming a lithographic printing plate by converting an image of undeveloped silver halide to be oleophilic, there has been proposed, for example, the treatment with an alkaline solution of a thiol compound (cf. U.S. Pat. No. 3,099,209), a terminal ethynyl compound (cf. U.S. Pat. No. 3,454,398) or an alkaline solution containing a benzotriazol compound (cf. U.S. Pat. No. 3,764,323). However, these prior treatments all have such defects that the receptivity of inks are too poor to produce a copy of sufficient density, long periods of time are required for permitting images to receive an ink or ink-receptive portions are worn out before a number of copies is produced.